The present invention relates to a motor control center having a frame which has a plurality of mounting sections open in one direction, a three-phase main bus, a three-phase branch bus and a plurality of units each mounted in the mounting section, supplied with power from said branch bus and supplying power to a predetermined load, each of said units comprising a floor plate, a first group of electrical appliances which requires relatively frequent inspection and maintenance, and a second group of electrical appliances which requires relatively infrequent inspection and maintenance.
A motor control center of the type described is already known in which a detachably mounted unit generally has a floor plate, an appliance mounting plate and a disconnecting part mounting plate. On said floor plate is mounted a unit drawing mechanism. On said appliance mounting plate are mounted main circuit appliances such as a main circuit disconnecting part, an electric meter, an electromagnetic contactor and a thermal relay; as well as circuit control appliances such as an auxiliary relay, an auxiliary transformer, control fuses and an indicating lamp. On said disconnecting part mounting plate are mounted a main output circuit disconnecting part, a disconnecting part for control circuit, an indicating lamp. In a conventional motor control center of this type, the various electrical appliances of each unit, such as the disconnecting parts, case circuit breakers, electromagnetic contactors, transformers, etc., are arranged on the floor plate with little thought for ease of maintenance and inspection. Further, when press button switch, indicating lamp, electric meter and release button (to be referred to collectively as third group of electric appliances hereinafter) are included in each unit, such third group are customarily arranged on the unit door which is mounted on the frame and covers the front surface of the unit and which is able to open and close, or on the wiring trough door mounted separately from each unit of the motor control center, or on both doors. This type of conventional motor control center is effective for supervision and control of many electric load circuits. Nevertheless, it presents the disadvantages described below which leave room for improvement. First, maintenance and inspection is inconvenient since various electrical appliances as mentioned above are arranged with little consideration for ease in maintenance and inspection. Second, since the third group of electrical appliances are scattered on the unit door and the wiring trough door described above, the design of these doors must be altered when a part of the circuit is changed.